Lightweight insulating concretes are known to be used as materials for roof deck surfaces, often in combination with a waterproof membrane covering secured with base ply fasteners. Concrete materials used for this purpose should be lightweight and relatively low density, in order to reduce the weight load applied to the existing building structure and to aid in insulating the building. LWIC may be used to fill in depressions in existing lightweight concrete roof deck surfaces and thereby correct water drainage characteristics that are undesirable; to repair joints in roof deck surfaces; or to repair other damage to the concrete roof deck, including cracks and holes left in the LWIC surface from removal of fasteners during replacement of the waterproofing membrane. Weight may also be a particular concern if the concrete roofing material is to be placed above an existing layer of concrete as a method of roofing repair.
Lightweight insulating concrete used for repairing patches, cracks, or the like, or when used as a material for re-roofing a concrete roof, should have several desirable characteristics. It should be relatively light weight, or low density, compared to structural concrete. It should be resistant to water intrusions from leaks in or around the waterproof membrane. It should exhibit low shrinkage of the applied layer in the vertical direction when applied and allowed to harden. It should have the ability to be "feather-edged" to a zero, or near-zero, thickness to blend that layer's edge with the existing LWIC layer. In addition, an important characteristic is the length of time the material will require to set before it will bear foot traffic and accept and hold base ply or other fasteners. It should also be sufficiently strong to effectively retain fasteners placed therein, yet not so strong early after application as to prevent such placement of fasteners.
It is known to repair joints, cracks and depressions by filling the desired area. A known material for doing so include wood fiber-reinforced gypsum plaster, combinations of Portland cement and lightweight aggregate, and a slurry of Portland cement and water. Combinations of Portland cement and lightweight aggregate may also be used for other repairs, such as to re-roof by placing a new layer above an existing substrate layer.
However, these materials have many disadvantages. Gypsum tends to set very quickly (within a few minutes) and is therefore difficult to screed and feather edge. Also, gypsum mixtures are resistant to insertion of fasteners and prone to softening upor exposure to water. They also exhibit significant shrinkage in the vertical direction. Portland cement and lightweight aggregate mixtures have a very long set time, and typically the re-roofing process cannot proceed through placement of the waterproof membrane for at least 24 to 72 hours. This creates a significant disadvantage in that, particularly if the building is currently occupied, there is no waterproof roofing material applied to the roof for this period of time, which can result in damage in case of rain. A further disadvantage of aggregate/Portland cement mixtures is that they cannot be reliably feather edged to a zero, or near-zero, thickness because the resultant surface is rough and the bond to the existing LWIC is erratic and unpredictable.
Slurries of Portland cement and water also have a long set time, and thus have the same disadvantages as the aggregate/Portland cement mixtures. These slurries also exhibit excessive curing and drying shrinkage, and erratic and unpredictable bond strength to the lightweight insulating concrete substrate to which they are applied. The shrinkage exhibited by Portland cement slurries and gypsum mixtures is undesirable because it can result in the material pulling away from structures projecting vertically from the concrete roof deck surface, and it also may undesirably affect the slope-to-drain conditions created by original application of the material.
Various formulations for lightweight insulating concretes are known. U.S. Pat. No. 4,293,341 to Dudley et al. discloses a LWIC containing lightweight aggregate, Portland cement, an air entraining agent, a dispersing agent and preferably an inert densifying particulate. Dudley et al. teaches use of either vermiculite, or less desirably, perlite, but does not disclose any particular combination thereof. U.S. Pat. No. 4,293,341 to Dudley et al. is incorporated herein in its entirety for all purposes. Dudley et al. also discloses the use of air entraining agents and polyelectrolytic sulfonate dispersing agents to improve the characteristics of the concrete. Dudley et al. does not disclose specific set times, or early compressive strengths of the finished concrete.
U.S. Pat. No. 3,795,653 to Aignesberger et al. discloses lightweight concrete containing lightweight filler particles that are coated with melamine formaldehyde condensation product containing sulfonic acid groups and thereafter mixed with cement. Aignesberger et al. discloses that expanded clay, polystyrene, perlite, vermiculite, pumice, slag, or the like may be used alone or in combination as filler particles, but does not disclose any specific combinations or ratios.
U.S. Pat. No. 3,989,534 to Plunguian et al. discloses a cellular composition useful for fire resistance, soundproofing and thermal insulation that is formed from a (1) mineral cement, such as gypsum cement, Portland cement, calcium aluminate cement or magnesia cement, (2) a film former, such as guar gum or bentonite, (3) a mixture of ionic and non-ionic surfactants, and (4) a lightweight aggregate such as perlite, vermiculite or hollow silicate spheres, and (5) air substantially in excess of that used in air entrainment of cement. Plunguian et al. does not disclose combinations of perlite and vermiculite.
Apart from LWICs, U.S. Pat. Nos. 5,542,538 and 5,718,758 to Breslauer disclose a premixed ultra-light mortar for use with clay and concrete tiles using ASTM C-332 aggregate such as vermiculite or perlite in place of sand, with a mortar cement made from portland cement, lime, air entraining agents and water repelling agents. Breslauer does not disclose combinations of perlite and vermiculite. U.S. Pat. Nos. 5,542,538 and 5,718,758 to Breslauer are incorporated herein in their entirety for all purposes. Breslauer does not disclose specific set times, or early compressive strengths of the finished concrete.
U.S. Pat. No. 4,159,302 to Greve et al. discloses a material for a fire door core, comprising 50-70 weight percent expanded perlite, and as minor ingredients, an organic binder to achieve desired flexural and compressive strength, set gypsums and set hydraulic cement, which may include unexpanded vermiculite, clay, and fibrous reinforcements. The material is compression-molded and finished into a fire door core.
U.S. Pat. Nos. 3,372,040 and 3,502,490 to Ware disclose fire- and heat-resistant cementitious plaster compositions including a naturally-occurring phosphate rock and shale containing P.sub.2 O.sub.5, and 0-50 weight percent exfoliated perlite or vermiculite or mixtures thereof. Ware does not disclose specific combinations or ratios of perlite to vermiculite, nor does Ware disclose the strength or density of the material, or set times.
None of the prior art formulations has all of the characteristics desired by the roofing industry for a lightweight insulating concrete having light weight, high strength, relatively short set times, water resistance, low shrinkage and the ability to be feather-edged.